Are you suffering from a bad case of the nines? Symptoms include running a first-time marathon, training harder and speeding up in races.
When adults approach a new decade in age (i.e., at ages 29, 39, 49 or 59), they change their behaviour in a particular way, according to Adam Alter of New York University’s Stern School of Business and Hal Hershfield of the Anderson School of Management at the University of California, Los Angeles (UCLA). "Nine-ending ages prompt end-of-decade crises that resemble midlife crises," they say.
The two professors analyzed six studies looking at exercise, extramarital affairs, and suicide rates among adults between the ages of 25 and 65 across dozens of countries and cultures. They found a universal search for existential meaning as biological birthday clocks ticked toward a new decade.
"There's evidence that people create meaning by striving more intently for goals — so we assumed they were running marathons with more intent (or training harder) when they were at nine-ending ages," Alter says.
Among the pair's findings, some constructive and some destructive:
- In a random sampling of first-time marathoners, there were 25% more “9-enders” than runners whose ages ended in any other digit.
- Runners ran races about 2% faster at ages 29 and 39 than during the two years before and after those ages.
- Men aged 29, 39, 49 and 59 were nearly 18% more likely than men at other ages to register on dating websites that cater to people who are seeking extramarital affairs; the trend was echoed among women, though not as intensely.
- Suicide rates were 2.4% higher among individuals whose age ended in a 9 than among people whose ages ended in any other digit.
Alter says he and his colleague didn't see gender differences in these studies; both men and women see nine-enders as a self-reflective prelude to a milestone birthday. Their research paper, People search for meaning when they approach a new decade in chronological age, is published in the Proceedings of the National Academy of Sciences.